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The latest overhead imagery of North Korea’s Yongbyon nuclear complex indicates that its 5-megawatt electric plutonium production reactor was recently restarted. The government had voluntarily shut down the reactor, which produced plutonium to fuel its nuclear weapons, as a negotiation concession to Washington in July 2007. When I visited Yongbyon in November 2010 with Stanford University colleagues, North Korean officials told us that they had decided to convert the Yongbyon complex from a military plutonium production facility into a civilian nuclear power facility. They showed us the construction site of a new experimental light-water reactor (ELWR) and a modern centrifuge facility. At that time, there was no more plutonium in the pipeline ready to be reprocessed.

The restart of the 5-megawatt reactor will strengthen North Korea’s weapons program by producing more plutonium. It may also improve Pyongyang’s negotiating position, giving it more to bargain away, if the six-party talks resume with South Korea, the United States, Russia, China, and Japan.

The unveiling of a modern centrifuge facility during our 2010 visit, ostensibly to produce fuel for the ELWR, appeared to confirm that North Korea’s plutonium route to the bomb was at a dead end. It currently has only 24 to 42 kilograms of plutonium, and it may have used 4 to 6 kilograms for the third nuclear test in February 2013. I, along with most analysts, concluded that North Korea had decided to expand its nuclear arsenal by developing highly enriched uranium (HEU) weapons. The size and sophistication of the centrifuge facility, as well as the timing of construction, indicated that it also had a clandestine facility—one that I suspected of producing some HEU.

A move to HEU, however, was puzzling since Pyongyang’s declared objective for the third test was to demonstrate that North Korea can make smaller and more sophisticated nuclear devices, ones that presumably can be mounted on its missiles. Plutonium is a more desirable bomb fuel for miniaturization, and I believe it’s what North Korea used in its first two nuclear tests. Nevertheless, I speculated that if Pakistani nuclear scientist A. Q. Khan had shared his country’s HEU warhead designs and test data it may have led Pyongyang to conclude that HEU provided a quicker and more assured path to miniaturization, in addition to being much easier to hide.

The 5-megawatt reactor remained in standby while North Korea’s nuclear specialists made impressive progress on the construction of the ELWR from the time we saw the reactor containment structure just barely emerging from its foundation in 2010, to the spring of 2013 when the exterior of the plant appeared to be complete. North Korea is now keeping the plutonium-bomb option alive with the 5-megawatt reactor restart. Meanwhile Pyongyang has demonstrated once again the adeptness of its technical specialists at nuclear operations. They adapted a new cooling system that will use the Kuryong river to provide cooling for both the ELWR and the restarted 5-megawatt reactor, instead of replacing the cooling tower they blew up in a symbolic gesture to Washington in 2008. They were also able to adapt unused uranium alloy fuel rods that had been stored since the 1994 Agreed Framework. And, they were able to coax the nearly 30-year-old 5-megawatt reactor back into operation after a long shutdown.

The most likely technical scenario is that the North Koreans will operate the restarted 5-megawatt reactor for two years with a full load of 8,000 fuel rods, cool this spent fuel and extract roughly 10 to 12 kilograms of plutonium within three years from the fall of 2013. They can likely repeat this cycle multiple times since they previously told me they expect the reactor to function for several more decades. Hence, we can expect Pyongyang to gain one bomb’s worth of plutonium per year as long as it stays on this path. Such a production rate does not constitute a game changer, but it would give North Korea more plutonium to test in order to refine its nuclear devices to fit on its missiles.

We were told that the ELWR was designed as a prototype electrical power reactor. I believe that is its primary purpose. However, we cannot rule out that Pyongyang could also use the reactor to annually produce 10 to 15 kilograms of plutonium suitable for nuclear weapons by changing the typical long electrical-power reactor burn cycle to a shorter one. This would require modifications to the Yongbyon reprocessing facility to handle ceramic instead of metallic spent fuel. Any use of the ELWR for weapon-grade plutonium production would be observable using satellite imagery.

A more troublesome alternative, however, would be if Pyongyang built a copy of the 50-megawatt reactor that was near completion in 1994, but then abandoned because of the Agreed Framework. It would have to start over since the original reactor is beyond repair, but I believe North Korea has the requisite materiel and skill to do so. Such a reactor construction project would be readily observable using satellite imagery and take at least five years to complete. The 10 bombs’ worth of plutonium this reactor could produce would be a game changer.

It is difficult to say what the 5-megawatt reactor restart tells us about the uranium enrichment program and the HEU path to the bomb because we know so little about the enrichment program. The North Koreans gave us only limited access in 2010 and, to my knowledge, no foreigners have been there since. It is possible that the North Koreans ran into greater-than-anticipated difficulty with the centrifuge program. After all, it has taken Iran much longer to bring on line what appear to be technically much less capable centrifuges. However, overhead imagery of the Yongbyon fuel fabrication facility shows an immense amount of construction and activity since 2009, implying that the centrifuge program is in full swing. Moreover, recent overhead imagery showed a doubling of the size of the centrifuge hall building we were shown in 2010, although we don’t know what has gone inside the hall.

Pyongyang is moving ahead on all nuclear fronts: It announced in an April 2 statement that it will adjust and alter the use of existing nuclear facilities to simultaneously stimulate the economy and build up nuclear armed forces, implying that it will promote both commercial and military nuclear programs. It underscored its commitment to nuclear energy by promoting the General Bureau of Atomic Energy to the status of government ministry. It is expanding its missile launch facilities. It has at least one new nuclear test tunnel ready to go. It has restarted its plutonium production reactor and continues to progress toward operation of the ELWR, likely to begin in late 2014 or early 2015. Notwithstanding Pyongyang’s bombastic rhetoric of March and April threatening a pre-emptive nuclear attack on the United States and South Korea, its Supreme People’s Assembly passed a law spelling out North Korea’s rights and obligations as a responsible nuclear weapons state.

In recent months, North Korean leader Kim Jong-un’s regime has reached out to engage Washington, albeit in fits and starts. South Korean President Park Gyeun-hye is at the same time reaching out to Pyongyang on economic cooperation while remaining resolute on denuclearization. Beijing and Pyongyang are advocating a return to the six-party talks, which ceased in 2009 when North Korea withdrew. Since taking over the regime in 2011, Kim Jong-un has strengthened the North’s bargaining position by expanding its nuclear program and conducting a successful space launch. He has also complicated negotiations immensely with the reactor restart. Prior to the restart, the other parties could have taken the end of plutonium production as a given, but now the reactor, the spent fuel and the reprocessing facility give Pyongyang more bargaining chits. Moreover, implementation of any agreement will be much more difficult. No plutonium in the pipeline meant no spent fuel. Now, negotiators will have to deal with what to do with 8,000 spent fuel rods. That proved to be a costly and controversial undertaking during the Agreed Framework, which broke down in 2003.

Denuclearization of the Korean peninsula must remain the goal, but it is a more distant one following these new developments. It will now be more challenging and costly, although not impossible, to get North Korea to agree to what I have called “the three no’s”—no more bombs (meaning no more plutonium and HEU); no better bombs (no nuclear testing and no missile launches); and no exports.